Increase Fat Content of the Diet
System: Sheep
Mainly applicable for: Intensive, in-house systems; basal diets with a low fat content leaving room for fat supplementation.
Not applicable or effective for: Extensive (traditional) grazing systems, or pastoral systems; a high initial fat content of the basal diet strongly limits the potential of supplemental fat as dietary fat should not exceed 5%.
Description
Supplementing fats, oils, or free fatty acids (saturated or (poly)unsaturated) to the ration or to concentrate feed, in order to reduce the enteric methane emission in the rumen. It also delivers a high energetic source to the animal. Different types of lipid can be fed, such as coconut oil, sunflower oil, palm oil, or ingredients with a very high oil content such as crushed oilseeds. They can be applied in different forms; the so-called unprotected forms exerting an effect on rumen fermentation versus the protected forms with minimal impact and interaction with rumen fermentation. Exceeding the maximum level of usage, in particular of unprotected forms, increases dietary fat content too much and negatively impacts rumen function, fibre digestion, and dry matter intake. For sheep generally a maximum dietary fat content of 5% (which is lower than dairy and beef cattle) is recommended to prevent negative impact on rumen function, fibre digestion, dry matter intake and productivity.
Mechanism of effect
Increasing the lipid content reduces enteric methane emissions, mainly due to i) increased digestive efficiency, as lipids are high in energy (and low in fibres); ii) inhibition of methanogenesis, as lipids reduce the growth and activity of methane-producing microbes; iii) an effect on cell-wall degradation and the rumen fermentation profile (type of volatile fatty acids and amount of hydrogen/methane produced) leading to less hydrogen production as substrate for methanogens. Adding lipids also leads to a lower nitrogen (N) content relative to the energy content of the diet, thereby reducing N excretion and ammonia and nitrous oxide emissions. Some lipids are associated with land use change (LUC) effects, such as palm oil or soybean oil from areas with deforestation risks.
Reference situation
Normal lipid content of a basal diet without any fat supplementation.
Legend
| ● – Small effect (<5%) | o – No effect |
| ●● – Medium effect (5-20%) | ● – Unfavourable effect |
| ●●● – Large effect (>20%) | ● – ● – Variable effect (depending on farm characteristics or way/level of implementation) |
Effect on total greenhouse gas (GHG) emissions
| Mean effect and range in kg CO2-equivalents | per kg product | per farm | |||
| Mean | Min-Max | Mean | Min-Max | Level of evidence | |
| Fat supplementation | ●● | N/A – ●● | ●● | N/A-●● | High |
Effect per emission source
| Mean effect on emission from | Manure | Animal | Feed and forage production | Barn & farm inputs | |||
| CH4 | N2O | CH4 | CO2 | N2O | LUC | CO2 | |
| Fat supplementation | ● | ●● | ● | ● | |||
*risk of an adverse effect (see ’cause of variable or unfavourable effect’)
Cause of variable or unfavourable effect
Fat supplementation
The methane mitigating effect may depend on the type of fat, the application form, the inclusion rate, diet composition, type of sheep (animal characteristics), and the degree of (un)saturation of fatt acids in the supplemented fat. The effect becomes larger with further increase of dietary fat, although the maximum level of usage of dietary fat should be taken into account. Use of unsaturated fatty acids (UFA) in the supplemented fat source may have an extra effect on rumen fermentation and methane (and have a different risk for trade-offs). The reduction is greater in rations with more concentrate feed relative to forage (Patra, 2013), possibly because of lower rumen pH (Zhou et al., 2015) and it might be that more fat can be supplemented in concentrate-rich rations compared to forage-rich rations.
| Literature references | Fat supplementation |
|---|---|
| Benaouda et al., 2023 | Prediction of enteric methane emissions by sheep using an intercontinental database |
| Nayak et al., 2015 | Management opportunities to mitigate greenhouse gas emissions from Chinese agriculture |
| Almeida et al., 2021 | Meta-analysis quantifying the potential of dietary additives and rumen modifiers for methane mitigation in ruminant production systems |
| Arndt et al., 2022 | Full adoption of the most effective strategies to mitigate methane emissions by ruminants can help meet the 1.5 °C target by 2030 but not 2050 |
| Takahashi et al, 2024 | Lipid supplementation with macadamia by-product reduces methane emissions by sheep |
| Torres et al, 2023 | Potential of nutritional strategies to reduce enteric methane emission in feedlot sheep: A meta-analysis and multivariate analysis |
| Grainger et al., 2011 | Can enteric methane emissions from ruminants be lowered without lowering their production? |
| Flores-Santiago et al., 2022 | Reduction of enteric methane production with palm oil: Responses in dry matter intake, rumen fermentation and apparent digestibility in sheep |
| Mao et al., 2009 | Effects of addition of tea saponins and soybean oil on methane production, fermentation and microbial population in the rumen of growing lambs |
| Yulianri Rizki Yanza et al., 2020 | The effects of dietary medium-chain fatty acids on ruminal methanogenesis and fermentation in vitro and in vivo: A meta-analysis |